Worldwide, the annual energy consumption in buildings for cooling already almost exceeds the adequate energy consumption for heating thereof. Optimisation of the energy balance is required in order to avoid increasing thermal stress in towns. Buildings must be planned accordingly such that passive cooling is effected instead of equipping them with electrical air-conditioning units.
Protection from overheating is still effected almost exclusively via conventional mechanical shading.
Recent methods, such as active switching (above all by means of electrochromism) have not proved to be successful to date. In addition to economic aspects, still unresolved technological questions are most certainly responsible for this. In Encyclopedia of Polymer Sciences and Technology by A. Seeboth/D. Lötzsch (2004), the use of thermochromic materials for temperature-controlled optical effects is described in detail.
Attempts have been made for decades to use thermotropic hydrogels or polymer blends for sun protection. Between 1950 and 1960, experiments were already performed in Munich zoo with thermotropic materials for sun protection. Further thermotropic materials which switch as a function of temperature or layers which permanently reflect solar radiation in the field of sun protection are known from U.S. Pat. No. 4,307,942, U.S. Pat. No. 6,440,592 and US 2005/147825.
In addition to previously unresolved technological questions, reaction mechanisms in the thermotropic systems which are used, inter alia chemical competing reactions, phase separations, phase transitions, which have certainly also not been understood up to the present, are a substantial reason for delays in introduction onto the market. Thus for example in EP 0 125 804, an aliphatic compound of the general formula CnHn+2 with n=5 to 30 is introduced as thermotropic monomers in a concentration between 0.5 and 10% by weight into a photohardening matrix polymer. Structures of this general formula are however not able to function as monomers in a polymer reaction. Monomers or monomeric compounds are, by definition, low-molecular, reactive molecules which can amalgamate to form molecular chains or networks, to form unbranched or branched polymers. Furthermore, a migration process of the homogeneously distributed aliphatic compound in the polymer matrix to the substrate surface is necessary, in particular also promoted by thermal stress. The thermotropic properties, based on the necessity for an anisotropic phase and produced in a concentration range up to 10% by weight have no long-term stability. It is furthermore described in EP 0 125 804 that the mixture must have a corresponding solubility for the thermotropic component in order to make possible a precipitation reaction. The dissolving of the thermotropic phase necessarily leads to the loss of the anisotropy which is based on intermolecular interactions of the individual thermotropic molecules amongst each other. In the subsequent crosslinking, caused kinetically and thermodynamically, the thermotropic component cannot be precipitated again quantitatively as a separate phase. Furthermore, hardening of the polymer matrix by exposure to light under an inert atmosphere or the production of films by casting between two glass plates and subsequent removal thereof does not permit continuous and cost-effective technology. This solution strategy is therefore not marketable.
The object underlying the invention, starting from the described disadvantages of the state of the art, is therefore to provide a thermotropic plastic material which has long-term stability, i.e. is thermodynamically stable, and can be used inter alia for sun protection.
This object is achieved by the features of the doping capsules and the composite system described herein, and the advantageous developments thereof. Uses according to the invention are also described.